Signaling system



Patented pr. 12, 1927.

UNITED STATES 1624579 PATENT OFFICE.

JOHN C. BURKHOLDER, O]? WEST END, NORTI-i CAROLINA, ASSIGNOR T0 XVES'IEEN ELECTBIC COMBANY, INCORIPORATED, OLENEW YORK, N. Y., A GORPORATION OZE NEW yonx.

SIGNLING SYSTEM...

Application fi1ed' January s, 1922. Serial N0. 527,097.

'lhis iny ntion relates to signaling systems and more partmularly to a carner eurrent system.

In the operation 0f carrier current sys Tuns heretofore deviseil, i t has been foiind l hat us the 'potentimnefuer inserted between Llie carrier wave sou1ce und the transmission queneies, an in most cases, causes considerable inter-ference between channels; while it also limits th e p0rtion 0f the frequency spectrum availableior Sigr 1al purposes.

The present'invention is directed to a circuit arrangemant involving aresistance network, adaptd t0 be used in place 0f *tl1e sending potentiometer, whigh functions to maintain the -impdance betwee'n the oscillator ancl the transmission line substantia'lly constant over the whole frequency range utilized 'for signal purposes. Glose.r spacing of the channels is therefo1e possible and impedance variations external to 'the 05011- lat0r circuit are prevented frbm reacting upon. the oscillator, t0 change '1ts frequency, whether the se variations are due to gain control adjustments, line disturbances, 01' other causes. 4 According to this invention, a resistance in series With the otentiometer resistance iS includecl in tl1 e oscillating current output circuit 0f the oscillahor andapair of resistances whibh are of equal value are 'connected 10etween tl1e terminals of tl1e otentiometer resistance and the adjustable contact associated 'withit. Thus each of tl1e equ al resistances is 'c0nnect6cl in parallel across one half 0f the potentiometer resistance through its-associatecl acljustable contact. As this contact is adjus'ted to include a greater amount of tl1e otentiometer resistan'ce in parallel with 011e of the equal resistance s and a lesser amount in parallel with the other, the out supply source.

put impedance relative t0 the line is varied and hence the voltage impressed upon =-the which will be clearly sei: forth in the folline'is changecl, VVl1ll the total impedance lowing description taken in connection With an oscillator ofth6 type describe d in United States Patent N0. 1,356763 to R. V. L.

Hgirtley, 0ctober 26, 1920. As illustrated, th1s osc1llator comprises an electron dischargedevide 1 pr0vided witl1 a heated cathode, a coritrolelement 01' grid, am]. an anode, having an inpt =circuit extending between the cathode and grid, an output circuit connecting the 'anode and g1id, und tl1ese circuits couplecl in feed-back relation. The coupling connection includes a tuned circuit consisting of a n inductance 2 shun'v ed by a c0ndenser 3, either, or bot-h 0f which may be varied, to determine tl1e frequency 0f the oscillationsgenerated. Obviously, an oscillator having the tune l frequency determining circui't included in either its input or outPut circuit may be'uged as a carrier The usual filament hea'ting and plate current sources 4 and 5 res'pective1y, and associated nontrol resistances therefore are provided, as are also blocking condensers 6 and a 'highiesistance 7. The blocking condenser 6 shunted by a high grid leak resistance serves in well known manner to maintain the grid 0f the oscillator at the proper negative potential While the tube 1 ance 01 network 8 through the resistance 9. The network 8 comprises resistances 10, 11, 12 und a contact 13 Which is adjustably associated with the resistance 10 and i s connected through the resistances 11 and 12 with the respective terminals 0f the resistance 10. The intensity of the electromotive. force impressed upon the input circuit of an zunplifiel 11 may be regulated by adju'sting the contact 13 to vary the portions 0f the resistance 10 connected in parallel w1th the resistances 11 and 12 respectively. In this manne1, while the otential dfop across that portion of the resistmceassociated with the input circuit of the amplifier 14 is varied, the total.resistance included in the oscillator output circuit is mai ntained substantiailly constant.

Heretofore with the well-known design of potentiometer the resistance of which was 0f the san1e order of magnitude as the individual resistances used in the network hereinbefore described, it was found necessary to give the resistance 9 included in the os'cil- 1ator output oircuit, a differen t value f01' the different fre'quency ranges used. For effective transmission over ranges up t0 5000 cycles, one value 0f resistance wasused and for ranges between 6000 and 10000 cycl es, a rosistance five times as great was employed.

As the contact of the potentiome ter was ad justed to give the necessary ga1n, so that signa1 impulses or trains 0f oscillations Cf ths required amplitude cou1d be supplied to the line for transmission to a distant receiving station, the frequency of the oscillator' varied to such an extent that the spacing beitween channels was seriously redutzd and as a result interferenoe betw.een the different sigma! channels occurred'.

' In an effort to eh'minate this interference, resort was ha to relativel'y larger channel' spacing, but even then, ii; was found necessary as.the potentiometer setting approziched the maximum voltage position to readjust the oscillator frequency to its original value in erde; tosecure efiicient transmission without interference.

' With a otentiometer of the design here'- in described, signa1ing may be carried on over all signa1 channels'without cha-nge in the value of the resistances included in the oscillator outPut circuit other than that due t0 the adjustment of the contact 18. N0 appreciable change of frequency occrs over the entire frequency range used in-carrier telegraph transmison. The frequency of each channe1 is substantially consta nt and as a consequence, the several channe1s may be more close1y spaced 011 the frequency Spectrum and hence a 1arger number 0f channels are therefore available 'f01 signaling purposes than in the circuit arrangernkents previously used. 'This arrangement is theref'ore especia11y adapte for 'use in a mu1tip'1ex carrier system, since once the tuned circuits 01 the oscillators f01 the respective channels have been set, the desired gain for each channel may b0 eflected UV adjusting the potentiometer.

Normally Carl'ier .waves are impressed upon theline und signal impulses 01 trains 0f oscillations a1"e transmitted to (istant receiving station by shunting the oscillating potential normally impressed upon the grld 01 control element of the, amplifier 14 through a path 0f low impedance :Eor the cm- 1-ier frquency. A circuit 15, connected across the input circuit 0f t'h0 amplifie1 141 und adapited to be controllad by a key, relay o1 other similar device, is shown :t'0'r this purpose. Resistance 9 serves to stabilize the oporation of the os cillator by preventing changes in the impedance o f the load circuit, when the low impedance path 15 is closed during signaling periodsf1om reacting thereupon. '1he output circuit 01 thc am plifier includes a tuned circuit coinprising the variable condonse'r 14. .coils 1 1", and the primary winding of a repeating coil o1 transfonner 17 means 0f which the amplifi'er output circuit is coupled to che 1ine 16. The usual heatingandp1ate sourcesas we11 as a bloc'zking condenser and choke coil are associated with the output circuit of the amplifiel 14.

A sending circuit including a Potentiometer 0f the type described above, having a resistance 10, provided with twenty-steps, operatecl between the eighth and thirteenth steps sind working into an artificial 10ad circuit .of two hundred ohms at twe1ve thousand qycles gave current of ten milliamperes at the output .ter1ninals of the 10ad circuit with the maximum Potentiometer setting employed whichdecreasbd about one milliampereper otentiometer 'step.= Hence at the midpoi'nt ofthe resistande l0the ou tput current was seVen miliiamperes which is adequate for' efiicient transmission. It was also found that t1m frequency chsmge over the entire potent1omster rang'e was not'more than ten Cyclos at an :Ereq1iency hetwen three thousand and ten t ousa nd cyb"es. A change of ten vo1ts in the p1ate battery of the oscillator caus@d 'the frequency o f the o scillator to vary fifteen cycles. A chan e 'of .1 ampere in theheating current for the 1ament produce'd a. frequency Variation of the waves genrated by the oscil1atoro:f five cyc1es. In this test die resistance7 was 24000 ohms and th81esistances While in this description certain specific etai1s have Deen sei forth with the object of clearly und completely disclosing the vurious features und method of opefation 0f the invention, lt is to b e understood that this inventio n is n0t; limited t0 these details, laut 0nly by the scope of tl1e zrttached claifns.

W hat is claimed is:

l. In combination, a sourue 0f oscillations und a transmision circuit connected to su1d source through a otentiometer wliich comprises a resistance, an adjustable c0ntact; as-

socizrted therewith, and equal impedance devices connected between the terminals 0f said resistance and saicl adjustable oontact.

2. A source 0f oscillations, a. transmisslon rlrcuit connectecl t0 said source through a polentiometer network comprising a plurality ufi resistances, a contzrct adjustably assoclated w1th one 0f sa1d resistances, the, other resistances being connected in parallel lvithsaid lirst mentioned resistance, ancl a connection from the cmmon terminal f said other resistances t0 said adjustable contzrct.

3. A sourc 0f oscil lations, a transmission clrcult connected to said sourco through a' I potentwmeter compnsmg a res1stance, an adnected to said adjustable contact.

5. A signal systemcomprising a source of oscillations, control means f0r shunting sai(l source, und. a potentiometer network counected between sa1 d source and sa1 l lmntmg meanscomprising a 1esistunce, an adjustablo c 0ntzlct. associated therewith, und asecoml re- 'sistance connected in parallel with said first resistance hzrving its mid-point connected t0 said adjustable contact.

In witness whereof, I hereunto subscribe my nam'e this 30th clay of Dec'ember, A. D. 1921. 1

JOHN 0. BURKHOLDER. 

